The present invention consists in a method of receiving voice signals transmitted by a base station to a mobile telephone, in particular a GSM mobile telephone. It is directed mainly to reducing the power consumption of mobile telephones when they are communicating but the other party is silent.
In the field of mobile telephones, the ability of a telephone to remain on standby or available for a long time period is essentially conditioned by the energy stored in its battery and by its power consumption. Because only limited energy can be stored in the battery, power saving is assured essentially by choosing low-dissipation components and by placing the mobile telephone on standby as often as possible. In standby mode, the power supply is disconnected from ancillary circuits of the mobile telephone. These ancillary circuits essentially comprise the keypad, screen, transmitter, and receiver. Also, the clock frequency of the microprocessor controlling the mobile telephone is reduced, typically from a few MHz to a few tens of kHz, which significantly reduces power consumption. The reduction is insufficient, however.
Mobile telephones available at present have a standby time in the range from around sixty hours to around one hundred hours. The talk time when the mobile telephone is transmitting and moving around is much shorter. In both cases the mobile telephone must nevertheless be available to receive speech signals or signaling. When the mobile telephone is on standby (not communicating), it must be able to receive signaling from a base station to advise it of an incoming call, i.e. that someone is attempting to call it. The mobile telephone must therefore be able regularly to receive signaling which tells it, firstly, at which agreed time information on a possible connection will next be sent to it and, secondly, whether it is currently being called by another party, so that it can begin to communicate immediately. The electrical power consumed in receiving such signaling limits the standby time referred to above.
This problem is solved by the technical solution described in patent application WO 98/13949, for example, in which advantage is taken of the highly redundant nature of the signaling by receiving only some of the signaling in a favorable situation and thereby placing the mobile telephone on standby for a long period of time.
During the call phase, the telephone may not need to transmit. However, whether it is transmitting or not, the mobile telephone must listen at all times for speech signals from the other party. The other party may be silent for a short while. It is estimated that in a normal call a mobile telephone transmits only half the time. The mobile telephone must be able to listen throughout the call, however. If the other party is silent while listening, and possibly even when the mobile telephone is itself transmitting, it is necessary to limit the power consumption associated with listening while the other party is silent.
In the discontinuous transmission (DTX) technique, which is well known in the art, the base station communicating with the mobile telephone transmits SID (Silence Identification Data) signaling corresponding to this situation. It may be feasible to use these SID signals to switch the mobile telephone to the standby mode, with low power consumption in receive mode, until SID signals are received again. However, this approach is not practicable because the other party may resume conversation with the mobile telephone at any time. In the final analysis, it is therefore necessary to listen between receiving SID signals to determine if the other party has started to speak again. This increases power consumption.
Given that the reduction in power consumption achieved so far has been insufficient, the invention seeks to reduce it further. The starting point is the realization that the information to be sent to a mobile telephone is coded in given-length blocks of bits. The bits of these blocks of bits are distributed across a plurality of windows in a plurality of successive frames to be routed to their destination.
In accordance with the invention, under these conditions, the choice is made to receive, in a first frame, speech signals or signaling transmitted in a first time window during the first frame. Receiving them involves demodulating them and possibly decoding them and in this case therefore entails activating the entire receive sub-system. This sub-system includes one or more voltage-controlled oscillators for receiving and demodulating received signals in baseband. The receive sub-system also includes a processor for decoding the bits received, in particular a Viterbi decoder. In accordance with the invention, the decoding is performed only if the demodulation is correct. Where applicable, this saves the non-negligible energy required to start the processor. Once this has been accomplished for signaling of at least a first time window, its meaning is considered. Before the next time window arrives, in principle in the same relative position in the next frame, the mobile telephone is or is not configured to receive the corresponding second speech signals or signaling.
Of course, when they are not received, neither demodulation nor processing is activated, which achieves a substantial energy saving.
The invention therefore consists in a method of receiving voice signals in a mobile telephone wherein said voice signals are divided into time windows in successive frames, said method including the following ordered steps:
first voice signals corresponding to a first time window are received,
the quality of the received signals is measured and compared to a first threshold, and
the mobile telephone is selectively configured to receive second voice signals corresponding to a second time window as a function of the quality information.
If necessary, the same processing is performed for a subsequent time window.